<?php
/////////////////////////////////////////////////////////////////
/// getID3() by James Heinrich <info@getid3.org>               //
//  available at http://getid3.sourceforge.net                 //
//            or http://www.getid3.org                         //
/////////////////////////////////////////////////////////////////
// See readme.txt for more details                             //
/////////////////////////////////////////////////////////////////
//                                                             //
// module.audio.ac3.php                                        //
// module for analyzing AC-3 (aka Dolby Digital) audio files   //
// dependencies: NONE                                          //
//                                                            ///
/////////////////////////////////////////////////////////////////


class getid3_ac3 extends getid3_handler
{
    private $AC3header = array();
    private $BSIoffset = 0;

    const syncword = "\x0B\x77";

    public function Analyze()
    {
        $info = & $this->getid3->info;

        ///AH
        $info['ac3']['raw']['bsi'] = array();
        $thisfile_ac3 = & $info['ac3'];
        $thisfile_ac3_raw = & $thisfile_ac3['raw'];
        $thisfile_ac3_raw_bsi = & $thisfile_ac3_raw['bsi'];


        // http://www.atsc.org/standards/a_52a.pdf

        $info['fileformat'] = 'ac3';

        // An AC-3 serial coded audio bit stream is made up of a sequence of synchronization frames
        // Each synchronization frame contains 6 coded audio blocks (AB), each of which represent 256
        // new audio samples per channel. A synchronization information (SI) header at the beginning
        // of each frame contains information needed to acquire and maintain synchronization. A
        // bit stream information (BSI) header follows SI, and contains parameters describing the coded
        // audio service. The coded audio blocks may be followed by an auxiliary data (Aux) field. At the
        // end of each frame is an error check field that includes a CRC word for error detection. An
        // additional CRC word is located in the SI header, the use of which, by a decoder, is optional.
        //
        // syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC

        // syncinfo() {
        // 	 syncword    16
        // 	 crc1        16
        // 	 fscod        2
        // 	 frmsizecod   6
        // } /* end of syncinfo */

        $this->fseek($info['avdataoffset']);
        $this->AC3header['syncinfo'] = $this->fread(5);

        if (strpos($this->AC3header['syncinfo'], self::syncword) === 0) {
            $thisfile_ac3_raw['synchinfo']['synchword'] = self::syncword;
            $offset = 2;
        } else {
            if (!$this->isDependencyFor('matroska')) {
                unset($info['fileformat'], $info['ac3']);
                return $this->error('Expecting "' . getid3_lib::PrintHexBytes(self::syncword) . '" at offset ' . $info['avdataoffset'] . ', found "' . getid3_lib::PrintHexBytes(substr($this->AC3header['syncinfo'], 0, 2)) . '"');
            }
            $offset = 0;
            $this->fseek(-2, SEEK_CUR);
        }

        $info['audio']['dataformat'] = 'ac3';
        $info['audio']['bitrate_mode'] = 'cbr';
        $info['audio']['lossless'] = false;

        $thisfile_ac3_raw['synchinfo']['crc1'] = getid3_lib::LittleEndian2Int(substr($this->AC3header['syncinfo'], $offset, 2));
        $ac3_synchinfo_fscod_frmsizecod = getid3_lib::LittleEndian2Int(substr($this->AC3header['syncinfo'], ($offset + 2), 1));
        $thisfile_ac3_raw['synchinfo']['fscod'] = ($ac3_synchinfo_fscod_frmsizecod & 0xC0) >> 6;
        $thisfile_ac3_raw['synchinfo']['frmsizecod'] = ($ac3_synchinfo_fscod_frmsizecod & 0x3F);

        $thisfile_ac3['sample_rate'] = self::sampleRateCodeLookup($thisfile_ac3_raw['synchinfo']['fscod']);
        if ($thisfile_ac3_raw['synchinfo']['fscod'] <= 3) {
            $info['audio']['sample_rate'] = $thisfile_ac3['sample_rate'];
        }

        $thisfile_ac3['frame_length'] = self::frameSizeLookup($thisfile_ac3_raw['synchinfo']['frmsizecod'], $thisfile_ac3_raw['synchinfo']['fscod']);
        $thisfile_ac3['bitrate'] = self::bitrateLookup($thisfile_ac3_raw['synchinfo']['frmsizecod']);
        $info['audio']['bitrate'] = $thisfile_ac3['bitrate'];

        $this->AC3header['bsi'] = getid3_lib::BigEndian2Bin($this->fread(15));
        $ac3_bsi_offset = 0;

        $thisfile_ac3_raw_bsi['bsid'] = $this->readHeaderBSI(5);
        if ($thisfile_ac3_raw_bsi['bsid'] > 8) {
            // Decoders which can decode version 8 will thus be able to decode version numbers less than 8.
            // If this standard is extended by the addition of additional elements or features, a value of bsid greater than 8 will be used.
            // Decoders built to this version of the standard will not be able to decode versions with bsid greater than 8.
            $this->error('Bit stream identification is version ' . $thisfile_ac3_raw_bsi['bsid'] . ', but getID3() only understands up to version 8');
            unset($info['ac3']);
            return false;
        }

        $thisfile_ac3_raw_bsi['bsmod'] = $this->readHeaderBSI(3);
        $thisfile_ac3_raw_bsi['acmod'] = $this->readHeaderBSI(3);

        $thisfile_ac3['service_type'] = self::serviceTypeLookup($thisfile_ac3_raw_bsi['bsmod'], $thisfile_ac3_raw_bsi['acmod']);
        $ac3_coding_mode = self::audioCodingModeLookup($thisfile_ac3_raw_bsi['acmod']);
        foreach ($ac3_coding_mode as $key => $value) {
            $thisfile_ac3[$key] = $value;
        }
        switch ($thisfile_ac3_raw_bsi['acmod']) {
            case 0:
            case 1:
                $info['audio']['channelmode'] = 'mono';
                break;
            case 3:
            case 4:
                $info['audio']['channelmode'] = 'stereo';
                break;
            default:
                $info['audio']['channelmode'] = 'surround';
                break;
        }
        $info['audio']['channels'] = $thisfile_ac3['num_channels'];

        if ($thisfile_ac3_raw_bsi['acmod'] & 0x01) {
            // If the lsb of acmod is a 1, center channel is in use and cmixlev follows in the bit stream.
            $thisfile_ac3_raw_bsi['cmixlev'] = $this->readHeaderBSI(2);
            $thisfile_ac3['center_mix_level'] = self::centerMixLevelLookup($thisfile_ac3_raw_bsi['cmixlev']);
        }

        if ($thisfile_ac3_raw_bsi['acmod'] & 0x04) {
            // If the msb of acmod is a 1, surround channels are in use and surmixlev follows in the bit stream.
            $thisfile_ac3_raw_bsi['surmixlev'] = $this->readHeaderBSI(2);
            $thisfile_ac3['surround_mix_level'] = self::surroundMixLevelLookup($thisfile_ac3_raw_bsi['surmixlev']);
        }

        if ($thisfile_ac3_raw_bsi['acmod'] == 0x02) {
            // When operating in the two channel mode, this 2-bit code indicates whether or not the program has been encoded in Dolby Surround.
            $thisfile_ac3_raw_bsi['dsurmod'] = $this->readHeaderBSI(2);
            $thisfile_ac3['dolby_surround_mode'] = self::dolbySurroundModeLookup($thisfile_ac3_raw_bsi['dsurmod']);
        }

        $thisfile_ac3_raw_bsi['lfeon'] = (bool)$this->readHeaderBSI(1);
        $thisfile_ac3['lfe_enabled'] = $thisfile_ac3_raw_bsi['lfeon'];
        if ($thisfile_ac3_raw_bsi['lfeon']) {
            //$info['audio']['channels']++;
            $info['audio']['channels'] .= '.1';
        }

        $thisfile_ac3['channels_enabled'] = self::channelsEnabledLookup($thisfile_ac3_raw_bsi['acmod'], $thisfile_ac3_raw_bsi['lfeon']);

        // This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1-31.
        // The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.
        $thisfile_ac3_raw_bsi['dialnorm'] = $this->readHeaderBSI(5);
        $thisfile_ac3['dialogue_normalization'] = '-' . $thisfile_ac3_raw_bsi['dialnorm'] . 'dB';

        $thisfile_ac3_raw_bsi['compre_flag'] = (bool)$this->readHeaderBSI(1);
        if ($thisfile_ac3_raw_bsi['compre_flag']) {
            $thisfile_ac3_raw_bsi['compr'] = $this->readHeaderBSI(8);
            $thisfile_ac3['heavy_compression'] = self::heavyCompression($thisfile_ac3_raw_bsi['compr']);
        }

        $thisfile_ac3_raw_bsi['langcode_flag'] = (bool)$this->readHeaderBSI(1);
        if ($thisfile_ac3_raw_bsi['langcode_flag']) {
            $thisfile_ac3_raw_bsi['langcod'] = $this->readHeaderBSI(8);
        }

        $thisfile_ac3_raw_bsi['audprodie'] = (bool)$this->readHeaderBSI(1);
        if ($thisfile_ac3_raw_bsi['audprodie']) {
            $thisfile_ac3_raw_bsi['mixlevel'] = $this->readHeaderBSI(5);
            $thisfile_ac3_raw_bsi['roomtyp'] = $this->readHeaderBSI(2);

            $thisfile_ac3['mixing_level'] = (80 + $thisfile_ac3_raw_bsi['mixlevel']) . 'dB';
            $thisfile_ac3['room_type'] = self::roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp']);
        }

        if ($thisfile_ac3_raw_bsi['acmod'] == 0x00) {
            // If acmod is 0, then two completely independent program channels (dual mono)
            // are encoded into the bit stream, and are referenced as Ch1, Ch2. In this case,
            // a number of additional items are present in BSI or audblk to fully describe Ch2.

            // This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1-31.
            // The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.
            $thisfile_ac3_raw_bsi['dialnorm2'] = $this->readHeaderBSI(5);
            $thisfile_ac3['dialogue_normalization2'] = '-' . $thisfile_ac3_raw_bsi['dialnorm2'] . 'dB';

            $thisfile_ac3_raw_bsi['compre_flag2'] = (bool)$this->readHeaderBSI(1);
            if ($thisfile_ac3_raw_bsi['compre_flag2']) {
                $thisfile_ac3_raw_bsi['compr2'] = $this->readHeaderBSI(8);
                $thisfile_ac3['heavy_compression2'] = self::heavyCompression($thisfile_ac3_raw_bsi['compr2']);
            }

            $thisfile_ac3_raw_bsi['langcode_flag2'] = (bool)$this->readHeaderBSI(1);
            if ($thisfile_ac3_raw_bsi['langcode_flag2']) {
                $thisfile_ac3_raw_bsi['langcod2'] = $this->readHeaderBSI(8);
            }

            $thisfile_ac3_raw_bsi['audprodie2'] = (bool)$this->readHeaderBSI(1);
            if ($thisfile_ac3_raw_bsi['audprodie2']) {
                $thisfile_ac3_raw_bsi['mixlevel2'] = $this->readHeaderBSI(5);
                $thisfile_ac3_raw_bsi['roomtyp2'] = $this->readHeaderBSI(2);

                $thisfile_ac3['mixing_level2'] = (80 + $thisfile_ac3_raw_bsi['mixlevel2']) . 'dB';
                $thisfile_ac3['room_type2'] = self::roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp2']);
            }

        }

        $thisfile_ac3_raw_bsi['copyright'] = (bool)$this->readHeaderBSI(1);

        $thisfile_ac3_raw_bsi['original'] = (bool)$this->readHeaderBSI(1);

        $thisfile_ac3_raw_bsi['timecode1_flag'] = (bool)$this->readHeaderBSI(1);
        if ($thisfile_ac3_raw_bsi['timecode1_flag']) {
            $thisfile_ac3_raw_bsi['timecode1'] = $this->readHeaderBSI(14);
        }

        $thisfile_ac3_raw_bsi['timecode2_flag'] = (bool)$this->readHeaderBSI(1);
        if ($thisfile_ac3_raw_bsi['timecode2_flag']) {
            $thisfile_ac3_raw_bsi['timecode2'] = $this->readHeaderBSI(14);
        }

        $thisfile_ac3_raw_bsi['addbsi_flag'] = (bool)$this->readHeaderBSI(1);
        if ($thisfile_ac3_raw_bsi['addbsi_flag']) {
            $thisfile_ac3_raw_bsi['addbsi_length'] = $this->readHeaderBSI(6);

            $this->AC3header['bsi'] .= getid3_lib::BigEndian2Bin($this->fread($thisfile_ac3_raw_bsi['addbsi_length']));

            $thisfile_ac3_raw_bsi['addbsi_data'] = substr($this->AC3header['bsi'], $this->BSIoffset, $thisfile_ac3_raw_bsi['addbsi_length'] * 8);
            $this->BSIoffset += $thisfile_ac3_raw_bsi['addbsi_length'] * 8;
        }

        return true;
    }

    private function readHeaderBSI($length)
    {
        $data = substr($this->AC3header['bsi'], $this->BSIoffset, $length);
        $this->BSIoffset += $length;

        return bindec($data);
    }

    public static function sampleRateCodeLookup($fscod)
    {
        static $sampleRateCodeLookup = array(
            0 => 48000,
            1 => 44100,
            2 => 32000,
            3 => 'reserved' // If the reserved code is indicated, the decoder should not attempt to decode audio and should mute.
        );
        return (isset($sampleRateCodeLookup[$fscod]) ? $sampleRateCodeLookup[$fscod] : false);
    }

    public static function serviceTypeLookup($bsmod, $acmod)
    {
        static $serviceTypeLookup = array();
        if (empty($serviceTypeLookup)) {
            for ($i = 0; $i <= 7; $i++) {
                $serviceTypeLookup[0][$i] = 'main audio service: complete main (CM)';
                $serviceTypeLookup[1][$i] = 'main audio service: music and effects (ME)';
                $serviceTypeLookup[2][$i] = 'associated service: visually impaired (VI)';
                $serviceTypeLookup[3][$i] = 'associated service: hearing impaired (HI)';
                $serviceTypeLookup[4][$i] = 'associated service: dialogue (D)';
                $serviceTypeLookup[5][$i] = 'associated service: commentary (C)';
                $serviceTypeLookup[6][$i] = 'associated service: emergency (E)';
            }

            $serviceTypeLookup[7][1] = 'associated service: voice over (VO)';
            for ($i = 2; $i <= 7; $i++) {
                $serviceTypeLookup[7][$i] = 'main audio service: karaoke';
            }
        }
        return (isset($serviceTypeLookup[$bsmod][$acmod]) ? $serviceTypeLookup[$bsmod][$acmod] : false);
    }

    public static function audioCodingModeLookup($acmod)
    {
        // array(channel configuration, # channels (not incl LFE), channel order)
        static $audioCodingModeLookup = array(
            0 => array('channel_config' => '1+1', 'num_channels' => 2, 'channel_order' => 'Ch1,Ch2'),
            1 => array('channel_config' => '1/0', 'num_channels' => 1, 'channel_order' => 'C'),
            2 => array('channel_config' => '2/0', 'num_channels' => 2, 'channel_order' => 'L,R'),
            3 => array('channel_config' => '3/0', 'num_channels' => 3, 'channel_order' => 'L,C,R'),
            4 => array('channel_config' => '2/1', 'num_channels' => 3, 'channel_order' => 'L,R,S'),
            5 => array('channel_config' => '3/1', 'num_channels' => 4, 'channel_order' => 'L,C,R,S'),
            6 => array('channel_config' => '2/2', 'num_channels' => 4, 'channel_order' => 'L,R,SL,SR'),
            7 => array('channel_config' => '3/2', 'num_channels' => 5, 'channel_order' => 'L,C,R,SL,SR'),
        );
        return (isset($audioCodingModeLookup[$acmod]) ? $audioCodingModeLookup[$acmod] : false);
    }

    public static function centerMixLevelLookup($cmixlev)
    {
        static $centerMixLevelLookup;
        if (empty($centerMixLevelLookup)) {
            $centerMixLevelLookup = array(
                0 => pow(2, -3.0 / 6), // 0.707 (-3.0 dB)
                1 => pow(2, -4.5 / 6), // 0.595 (-4.5 dB)
                2 => pow(2, -6.0 / 6), // 0.500 (-6.0 dB)
                3 => 'reserved'
            );
        }
        return (isset($centerMixLevelLookup[$cmixlev]) ? $centerMixLevelLookup[$cmixlev] : false);
    }

    public static function surroundMixLevelLookup($surmixlev)
    {
        static $surroundMixLevelLookup;
        if (empty($surroundMixLevelLookup)) {
            $surroundMixLevelLookup = array(
                0 => pow(2, -3.0 / 6),
                1 => pow(2, -6.0 / 6),
                2 => 0,
                3 => 'reserved'
            );
        }
        return (isset($surroundMixLevelLookup[$surmixlev]) ? $surroundMixLevelLookup[$surmixlev] : false);
    }

    public static function dolbySurroundModeLookup($dsurmod)
    {
        static $dolbySurroundModeLookup = array(
            0 => 'not indicated',
            1 => 'Not Dolby Surround encoded',
            2 => 'Dolby Surround encoded',
            3 => 'reserved'
        );
        return (isset($dolbySurroundModeLookup[$dsurmod]) ? $dolbySurroundModeLookup[$dsurmod] : false);
    }

    public static function channelsEnabledLookup($acmod, $lfeon)
    {
        $lookup = array(
            'ch1' => (bool)($acmod == 0),
            'ch2' => (bool)($acmod == 0),
            'left' => (bool)($acmod > 1),
            'right' => (bool)($acmod > 1),
            'center' => (bool)($acmod & 0x01),
            'surround_mono' => false,
            'surround_left' => false,
            'surround_right' => false,
            'lfe' => $lfeon);
        switch ($acmod) {
            case 4:
            case 5:
                $lookup['surround_mono'] = true;
                break;
            case 6:
            case 7:
                $lookup['surround_left'] = true;
                $lookup['surround_right'] = true;
                break;
        }
        return $lookup;
    }

    public static function heavyCompression($compre)
    {
        // The first four bits indicate gain changes in 6.02dB increments which can be
        // implemented with an arithmetic shift operation. The following four bits
        // indicate linear gain changes, and require a 5-bit multiply.
        // We will represent the two 4-bit fields of compr as follows:
        //   X0 X1 X2 X3 . Y4 Y5 Y6 Y7
        // The meaning of the X values is most simply described by considering X to represent a 4-bit
        // signed integer with values from -8 to +7. The gain indicated by X is then (X + 1) * 6.02 dB. The
        // following table shows this in detail.

        // Meaning of 4 msb of compr
        //  7    +48.16 dB
        //  6    +42.14 dB
        //  5    +36.12 dB
        //  4    +30.10 dB
        //  3    +24.08 dB
        //  2    +18.06 dB
        //  1    +12.04 dB
        //  0     +6.02 dB
        // -1         0 dB
        // -2     -6.02 dB
        // -3    -12.04 dB
        // -4    -18.06 dB
        // -5    -24.08 dB
        // -6    -30.10 dB
        // -7    -36.12 dB
        // -8    -42.14 dB

        $fourbit = str_pad(decbin(($compre & 0xF0) >> 4), 4, '0', STR_PAD_LEFT);
        if ($fourbit{0} == '1') {
            $log_gain = -8 + bindec(substr($fourbit, 1));
        } else {
            $log_gain = bindec(substr($fourbit, 1));
        }
        $log_gain = ($log_gain + 1) * getid3_lib::RGADamplitude2dB(2);

        // The value of Y is a linear representation of a gain change of up to -6 dB. Y is considered to
        // be an unsigned fractional integer, with a leading value of 1, or: 0.1 Y4 Y5 Y6 Y7 (base 2). Y can
        // represent values between 0.111112 (or 31/32) and 0.100002 (or 1/2). Thus, Y can represent gain
        // changes from -0.28 dB to -6.02 dB.

        $lin_gain = (16 + ($compre & 0x0F)) / 32;

        // The combination of X and Y values allows compr to indicate gain changes from
        //  48.16 - 0.28 = +47.89 dB, to
        // -42.14 - 6.02 = -48.16 dB.

        return $log_gain - $lin_gain;
    }

    public static function roomTypeLookup($roomtyp)
    {
        static $roomTypeLookup = array(
            0 => 'not indicated',
            1 => 'large room, X curve monitor',
            2 => 'small room, flat monitor',
            3 => 'reserved'
        );
        return (isset($roomTypeLookup[$roomtyp]) ? $roomTypeLookup[$roomtyp] : false);
    }

    public static function frameSizeLookup($frmsizecod, $fscod)
    {
        $padding = (bool)($frmsizecod % 2);
        $framesizeid = floor($frmsizecod / 2);

        static $frameSizeLookup = array();
        if (empty($frameSizeLookup)) {
            $frameSizeLookup = array(
                0 => array(128, 138, 192),
                1 => array(40, 160, 174, 240),
                2 => array(48, 192, 208, 288),
                3 => array(56, 224, 242, 336),
                4 => array(64, 256, 278, 384),
                5 => array(80, 320, 348, 480),
                6 => array(96, 384, 416, 576),
                7 => array(112, 448, 486, 672),
                8 => array(128, 512, 556, 768),
                9 => array(160, 640, 696, 960),
                10 => array(192, 768, 834, 1152),
                11 => array(224, 896, 974, 1344),
                12 => array(256, 1024, 1114, 1536),
                13 => array(320, 1280, 1392, 1920),
                14 => array(384, 1536, 1670, 2304),
                15 => array(448, 1792, 1950, 2688),
                16 => array(512, 2048, 2228, 3072),
                17 => array(576, 2304, 2506, 3456),
                18 => array(640, 2560, 2786, 3840)
            );
        }
        if (($fscod == 1) && $padding) {
            // frame lengths are padded by 1 word (16 bits) at 44100
            $frameSizeLookup[$frmsizecod] += 2;
        }
        return (isset($frameSizeLookup[$framesizeid][$fscod]) ? $frameSizeLookup[$framesizeid][$fscod] : false);
    }

    public static function bitrateLookup($frmsizecod)
    {
        $framesizeid = floor($frmsizecod / 2);

        static $bitrateLookup = array(
            0 => 32000,
            1 => 40000,
            2 => 48000,
            3 => 56000,
            4 => 64000,
            5 => 80000,
            6 => 96000,
            7 => 112000,
            8 => 128000,
            9 => 160000,
            10 => 192000,
            11 => 224000,
            12 => 256000,
            13 => 320000,
            14 => 384000,
            15 => 448000,
            16 => 512000,
            17 => 576000,
            18 => 640000
        );
        return (isset($bitrateLookup[$framesizeid]) ? $bitrateLookup[$framesizeid] : false);
    }


}
